Method for preparing silicon nanocomposite dispersion using plasma, and anode active material and lithium secondary battery using same

ABSTRACT

The present invention relates to a method for easily producing nanoparticles by expansion, explosion, vaporization, condensation and cooling of plasma in a liquid by means of heat resistance and, more particularly, to a method for preparing a silicon nanocomposite dispersion having a uniform carbon layer coated on the surface of silicon of which at least one area is connected to a silicon carbide formed by reacting a carbon in liquid (C) during expansion, explosion, vaporization, condensation and cooling, and applied products thereof.

TECHNICAL FIELD

The present invention relates to a method for preparing a siliconnanocomposite dispersion and an anode preparation, and a lithiumsecondary battery using the same, wherein a silicon carbide is bonded toat least one region using a plasma, and a carbon layer-coated siliconnanoparticle is employed.

BACKGROUND ART

As an industrial trend is fast changing to an IT industry, anenvironment friendly energy industry and an electric vehicle industry,the demand for a lithium secondary battery as a power device is greatlyincreasing. Moreover, as an electronic device becomes compact-sized, thedevelopment on a high output and high energy density active substance,which may substitute a conventional electrode material of a lithiumsecondary battery, is widely underway.

In case of an anode, a theoretical capacity of graphite used for most ofcommercial lithium secondary batteries is about 372 mAh/g, and aninter-layer spreading speed of lithium is slow, for which a high speedcharging and discharging are limited. A silicon composite anode materialis gaining a great attention, which may be used to resolve theaforementioned problem and have been as an active substance for the past20 years, wherein the theoretical capacity thereof is about 4200 mAh/g.In case of a silicon-graphite composite anode material, the developmentthereon is intensively underway in the related industry for the sake ofan actual commercialization; however there still is a limit whencompeting with a conventional graphite in terms of its manufacturingprocess cost even though a good energy density and an enhanced chargingand discharging service life.

In order to resolve a mechanical damage to an electrode and a fastservice life decrease problem when using a silicon, which occur due to avolume expansion and contraction as it is repeatedly charged anddischarged, like most of metallic substances which are electrically andchemically alloyed with lithium, it needs to increase performancethrough a nano-sized particle preparation, a nano-structuralconfiguration, a nano-composite configuration and a complexation with alithium activation/deactivation hetero-material.

Most of the researches focused on the preparation of a nano-sizedsilicon anode are being carried out, mainly, based on a mechanicalcrushing and a complexation, a vapor synthesizing method, asolution-based chemical synthesizing method, etc. Good results on thecharacteristic of a secondary battery anode are being reported; howeverthere still is a problem in the way that a complicated process involvedin a synthesis, a high material cost, an input of impurities, a wastething treatment cost, an oxide production which is inevitably entailedduring a synthesizing process, which makes hard to actually use it as amaterial for commercialization.

The high energy plasma technology of an electric explosion is referredto a massive synthesis technology of powder, and it has been developedfor a long time. In recent years, an in-liquid electric explosiontechnology with respect to a semiconductor material has been developed(an application number 10-2008-0126028), which shows that a silicon mayelectrically explode in liquid; however the silicon is oxidized intoSiO₂ in an aqueous solution, for which the silicon is not appropriate asan anode active substance for a lithium secondary battery.

DISCLOSURE OF INVENTION

The present invention is made in an effort to resolve the aforementionedproblems. Accordingly, it is an object of the present invention toprovide a method for preparing a silicon nanocomposite dispersionwherein a silicon carbide is bonded to at least one region, and a carbonlayer-coated silicon nanoparticles is employed.

It is another object of the present invention to provide a method forpreparing a silicon nanocomposite powder using a silicon nanocompositedispersion.

It is further another object of the present invention to provide ananode and a lithium secondary battery formed of a silicon nanocompositepowder prepared by the aforementioned method.

To achieve the above objects, there is provided a silicon nanocompositewherein a silicon nanoparticle is formed by a plasma energy in anorganic solvent using a silicon material, and a silicon carbide isbonded to the surface of a particle or a carbon layer is coated thereon.

To achieve the above objects, there is provided a method for preparing asilicon nanocomposite dispersion wherein a silicon nanoparticle isformed in such a way to supply 5˜20 kV voltages to a silicon materialthrough an electrode using a plasma generator in an organic solvent andat the same time, a silicon carbide is bonded or a carbon layer iscoated.

To achieve the above objects, there is provided a method for preparing asilicon nanocomposite powder in such a way to carry out a filtering, acentrifugation, a drying, a heat treatment, a disintegration, adisperse, a classification, etc.

To achieve the above objects, there are provided a silicon nanocompositeanode formed of an anode active substance including a siliconnanocomposite powder, a conduction material, and an anode materialhaving a binder, and a lithium secondary battery made using the same,which has a low anode expansion ratio and a good room temperatureservice life characteristic and a good initial charging and dischargingcharacteristic.

Advantageous Effects of the Invention

The method for preparing a silicon nanocomposite dispersion according tothe present invention allows to provide a particle powder having an evengranule, wherein a process is simplified, and an inputted energy issmall, and a mass production is available at a low cost.

Moreover, the silicon nanocomposite dispersion prepared by theaforementioned preparing method is easy to use and is environmentallyfriendly since particles are dispersed in a liquid phase solvent.

In addition, the lithium secondary battery may resolve a fast servicelife decrease problem which occurs due to a reaction between an anodeactive substance made of a silicon nanocomposite powder and a lithium.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a photo showing a disperse stability of a siliconnanocomposite dispersion prepared according to the present invention.

FIG. 2 is a TEM photo showing an anode active substance preparedaccording to the present invention.

FIG. 3 is a XRD showing an anode active substance prepared according tothe present invention.

FIG. 4 is a lattice photo of a TEM showing a silicon carbide bonded to aparticle prepared according to the present invention.

FIG. 5 is a TEM photo showing the thickness of a silicon carbide bondedto a particle prepared according to the present invention.

FIG. 6 is a view showing a room temperature service life characteristic(a capacity, mAh/g) of a lithium secondary battery prepared according tothe present invention.

FIG. 7 is a view showing a room temperature service life (an efficiency%) of a lithium secondary battery prepared according to the presentinvention.

FIG. 8 is a view showing a room temperature service life (a capacitypreservation ratio %—a service life @100 times) prepared according tothe present invention.

FIG. 9 is a view showing an anode expansion ratio of a lithium secondarybattery prepared according to the present invention.

FIG. 10 is a view showing an initial charging and dischargingcharacteristic of a lithium secondary battery prepared according to thepresent invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Before the descriptions of the present invention, it should beunderstood that the terms used throughout the specification are meant todescribe a specific embodiment, not meant to limit the scope of thepresent invention which is limited by only the claims. All technicalterms and science terms used throughout the specification should beinterpreted as having the same meanings as a person having ordinaryskill in the art understands.

Throughout the specification and claims, unless otherwise stated theterms (comprise, comprises, comprising) mean “including a thingmentioned before, a step or a thing of a group and a step”, not used toexclude any of a predetermined thing, a step or a thing of a group or astep of a group.

Meanwhile, unless it is stated to the contrary, various embodiments ofthe present invention may be combined with other embodiments. Inparticular, a predetermined feature which is considered as beingpreferred or advantageous, may be combined with a predetermined featureor features. The embodiments and effects of the present invention willbe described.

A method for preparing a silicon nanocomposite and a dispersion for ananode active substance.

The present invention is referred to a silicon nanocomposite for ananode active substance wherein a silicon carbine is combined with atleast one region of a silicon nanoparticle surface or a carbon layer isemployed, and a method for preparing a silicon nanocomposite dispersionusing a plasma in an organic solvent.

A silicon nanoparticle may be obtained from a silicon material, and anaverage size thereof is 50˜300 nm in diameter. If the size is less than50 nm, a silicon carbine may be easily made due to a strong activationof a silicon (Si) nanoparticle, for which it may not be used as abattery active substance, and if the size is over 300 nm, an expansionratio may increase during a charging and discharging of a secondarybattery, for which it is not appropriate for an actual use. It ispreferred that the size thereof is 100 to 200 nm.

The silicon carbine bonding or carbon layer may be obtained from asilicon material and an organic solvent. The thickness of a siliconcarbine bonding is 0.1˜0.5 nm. If the thickness of the silicon carbinebonding is less than 0.1 nm, it is hard to obtain a strength strongenough to inhibit the expansion from a charging and discharging, and ifthe thickness thereof is over 0.5 nm, a charging or discharging may belimited due to a strong strength. For this reason, 0.2 to 0.3 nm ispreferred. The thickness of a carbon layer is 3˜15 nm. The siliconnanoparticle formation and the silicon carbine bonding or the carbonlayer may become a plasma state due to a high voltage pulse current inthe organic solvent and may finally form a silicon nanoparticle and atthe same time may form a silicon carbine bonding or a carbon layer. Thesilicon carbine bonding has a function to reduce the anode expansion asthe lithium secondary battery is repeatedly charged or discharged, andthe carbon layer has a function to prevent the oxidation of a siliconnanoparticle.

In the silicon nanocomposite, a silicon carbine bonding may be formed atone or more than one region of the silicon nanoparticle surface, and thesurface area where the silicon carbide bonding is formed, as compared tothe whole surface area of the silicon nanoparticle is 10˜50%, andpreferably 15˜30%. If it is less than 10%, the effect of lowering ananode expansion ratio may be very low, and if it is over 50%, the inputof the lithium ion may be interrupted, thus lowering the efficiency ofthe lithium secondary battery. The carbon layer may be formed with 3˜15nm on the surface of the silicon nanoparticle or the silicon carbidebonding.

The method for preparing a silicon nanocomposite dispersion will bedescribed in detail. The method for preparing a silicon nanocompositedispersion may include, but is not limited to, (a) connecting a siliconmaterial between a first electrode and a second electrode of a plasmagenerator in an organic solvent, and (b) supplying the voltage of 5˜20kV to the first electrode and the second electrode, wherein the step (b)may include (b-1) forming the silicon material with a siliconnanoparticle, and (b-2) forming a silicon carbide bonding or a carbonlayer on at least one region of the surface of the silicon nanoparticle.

The parts by weight of the silicon material with respect to 100 parts byweight of the organic solvent is 1-20 [1 wt %˜20 wt %]. If it is lessthan 1, a problem may occur in a yield. If it is over 20, a problem mayoccur, for example, a collision and an impact due to an interferencewith the previously produced particles owing to an increased density ina reactor, for which a surface damage and an increase fine particle mayincrease. More preferably, it is 3˜7 parts by weight.

The organic solvent may include one or more of alcohols and material formixing and may further include a dispersion agent, a surfactant and acarbon precursor. If a polyvinylpyrrolidone is added, a coagulation andprecipitation of a prepared silicon nanocomposite are available. Thepolyvinylpyrrolidone may be added 0.01˜1.0 parts by weight with respectto 100 parts by weight of the organic solvent, and the addition by0.01˜0.7 parts by weight is preferred, but it is not limited thereto.FIG. 1 shows a disperse stability of a dispersion (OPVP) containing apolyvinylpyrrolidone and a dispersion (NPVP) which does not contains thesame. In case of the dispersion not containing the polyvinylpyrrolidone,a silicon nanocomposite was isolated after 24 hours, and in case of thedispersion containing the polyvinylpyrrolidone, it was confirmed thatthe silicon nanocomposite was evenly dispersed after 24 hours. Ifmanufactured in the organic solvent, it is possible to prevent an overoxidation into SiO₂, which is different from the manufacturing in anorganic solvent.

The silicon material is referred to a material containing an inorganicsubstance which has been processed in the form of a wire or a rod. Theinorganic material may include one or more than one selected from agroup consisting of a silicon, a silicon powder, a metallic mixed powderof a metal different from the silicon, a silicon inorganic mixture, asilicon alloy, a silicon wafer, and a waste slurry or a siliconinorganic mixture produced from a silicon process.

The plasma generator is configured to transfer the voltage of 5˜20 kV toa silicon material through the electrodes and organic solvent in thechamber. More specifically, an electric energy will be charged to acapacitor which is referred to a high voltage charger, and upon anelectrode switch being connected, the discharging is started, and thesilicon material will be heated and turn into a plasma state, afterwhich a silicon nanoparticle can be finally produced. The increase in aresistivity due to an increased temperature of the silicon material maycontribute to spatially concentrating an energy consumption at theportion of a silicon material, thus producing a silicon nanoparticle. Atthe same time, a silicon carbide bonding and a carbon layer may beformed through a vaporization and condensation due to the instantgeneration of plasma and a resistive heating, and a siliconnanocomposite dispersion containing the same can be prepared. If theplasma power is less than 5 kV, a nanoparticle formation may be hard,and if it is over 20 kV, the nanoparticles of less than 50 nm may bemass-produced, so a silicon nanocomposite produced as the silicon of ahigh activity meets a carbon source may be turned into SiC a lot, forwhich it is not effective as an anode active substance.

As the thusly prepared silicon material is loaded, and the charging anddischarging are repeatedly carried out, a silicon nanocompositedispersion containing the particles of tens to thousands of grams can beprepared.

According to a method for preparing a silicon nanocomposite dispersion,a particle powder having an even granule can be obtained, and theprocess is simplified, and other chemical agents are not necessaryexcept for the organic solvent and the dispersing agent, for which theprocess of the present invention is referred to a process producing lessby-products and wastes. Since a vaporization and a plasma generation andextinction occur within tens of micro seconds, an actually suppliedenergy may be only 2˜5 times of the vaporization energy of the silicondespite of an initial high voltage and an instant large current, whichmakes it possible to greatly reduce the energy consumption whengenerating particles, and a mass production can be available at a lowercost.

In the silicon nanocomposite dispersion prepared by the preparationmethod of the present invention, since the particles are dispersed inthe organic solvent, which allows for an easier use, and since they arenot discharged into the air, the preparation method of the presentinvention is environmentally friendly, and the environment and humanbody are less exposed to harmful environments.

A method for preparing a silicon nanocomposite powder for an anodeactive substance.

This method is referred to a method for preparing a siliconnanocomposite powder for an anode active substance in such a way toisolate a silicon nanocomposite dispersed in a silicon nanocompositeprepared by the present invention. More specifically, the methodtherefor may include, but is not limited to, obtaining a siliconnanocomposite slurry in such a way to filter a silicon nanocompositedispersion prepared by the present invention and to centrifugallyisolate the filtered dispersion; vacuum-drying the silicon nanocompositeslurry at 50˜100° C.; and carrying out a high temperature heat treatmentwith respect to the dried silicon nanocomposite at 900˜1200° C. under aninert environment (an argon); and disintegrating, dispersing andclassifying the heat-treated silicon nanocomposite, through which asilicon nanocomposite powder for an anode active substance can beprepared.

The high temperature heat treatment is preferably carried out at900˜1200° C.

The silicon nanocomposite powder prepared by the aforementioned methodmay remain in a state where a silicon nanocomposite is coagulated, andthe size of the silicon nanocomposite powder in the coagulated state is1˜500 μm.

A silicon nanocomposite anode.

This anode is referred to an anode formed of an anode active substancecontaining over 5% by weight of the silicon nanocomposite powderprepared by the present invention, a conduction material, a binder andan anode material including a filler.

The anode active substance may be added by 5˜80 parts by weight withrespect to 100 parts by weight of the anode material containing an anodeactive substance. Preferably, it is added by 70˜80 parts by weight. Theanode active substance may be formed of an anode active substance, whichis able to occlude or discharge a lithium ion in addition to a lithiumtitanium oxide, for example a carbon, for example, a hard-graphitizedcarbon, a graphite carbon, etc.; a metallic complex oxide, for example,LixFe2O3(0≤x≤1), LixWO2(0≤x≤1), SnxMe1-xMe′yOz (Me: Mn, Fe, Pb, Ge; Me′:Al, B, P, Si, a group-1 element, a group-2 element and a group-3element, a halogen; 0<x≤1; 1≤y≤3; 1≤z≤8); a lithium metal, a lithiumalloy, a silicon alloy, a tin alloy; a metallic oxide, for example, SnO,SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3,Bi2O4, and Bi2O5; a conductive polymer, for example, a poly acetylene;and a Li—Co—Ni material.

The lithium secondary battery using an anode material according to thepresent invention employs as an anode active material the siliconcarbide bonding and the carbon-coated silicon nanocomposite, thusinhibiting an anode expansion, by which it is possible to provide aspecific capacity of 1400 mAh/g which is higher than 800 mAh/g of aspecific capacity of the lithium secondary battery made of an anodeactive material prepared by the conventional preparing method of theKorean patent registration number 10-1142534. In the present invention,the expansion ratio of the silicon may be inhibited within 10˜50%, so itis possible to provide a high capacity and high efficiency lithiumsecondary battery wherein the silicon anode active material is able toaccount for 5˜80% as compared to the conventional technology wherein theanode active material can be added within 3˜5%.

The anode may be prepared in such a way that an anode material-mixedsolution prepared by mixing an anode material in a solvent, for example,a n-methyl pyrrolidone (NMP) is coated on an anode current collector andis dried, and is subjected to a rolling work.

The anode current collector, in general, is made with a thickness of3˜500 μm. The type of this anode current collector is not limited aslong as it does not cause any chemical change to a correspondingbattery, and it has a conductivity. For example, it may be made, forexample, of a copper, a stainless steel, an aluminum, a nickel, a titan,a plasticized carbon, a material made by processing the surface of acopper or a stainless steel with a titan, a silver, etc., and an allotof an aluminum and a cadmium. The cathode current collector is able toenhance the bonding force of an anode active substance by forming smallprotrusions on the surface thereof. It may be implemented in variousforms, for example, a film, a sheet, a foil, a net, a porous body, afoamed body, a nonwoven cloth, etc.

The conductive material may be added by 1˜10% by weight with respect tothe whole weight of the mixture including an anode active substance. Thetype of the conductive agent is not limited to as long as it has apredetermined conductivity while not causing a chemical change to acorresponding battery. For example, it may be formed of any of agraphite, for example, a natural graphite or an artificial graphite; acarbon black, for example, a carbon black, a super-p, an acetyleneblock, a Khenchen black, a channel black, a furnace black, a lamp black,a summer black, etc.; a conductive fiber, for example, a carbon, ametallic fiber, etc.; a conducive whiskey, for example, a zinc oxide, apotassium titanate, etc.; a conductive metallic oxide of a titaniumoxide, etc.; and a conductive material, for example, a polyphenylene,etc.

The binder is a component which may assist the bonding of an anodeactive substance and a conductive material and the bonding with respectto an anode current collector and may be added by 1˜10% by weight withrespect to the whole wrights of the mixture including an anode activesubstance. The binder may be any of a PVDF, a PVA, a CMC, a starch, ahydroxypropyl cellulose, a recycled cellulose, a polyvinylrrolidone, atetrafluoroethylene, a PE, a PP, an EDPM, a sulfonate EPDM, a styrenebutyrene rubber, a fluorine rubber, various polymers, etc.

The filler may be a component which is able to inhibit the expansion ofan anode and may be selectively used. The type of the filler is notlimited to as long as it is a fibrous material, while not causing achemical change to the battery. For example, it may be any of an olefinpolymer, for example, a polyethylene, a polypropylene, etc.; and afibrous substance, for example, a glass fiber, a carbon fiber, etc.

A lithium secondary battery.

This is referred to a lithium secondary battery which may be formed of aseparator, an electrolyte and a cathode according to the preparingmethod of a typical lithium secondary battery using a siliconnanocomposite anode according to the present invention.

Referring to FIGS. 6 to 10, the lithium secondary battery made of asilicon anode active substance including a silicon carbide bonding and acarbon layer-coated silicon nanocomposite has an anode expansion ratiowhich is lowered to 10˜50% thanks to the physical and mechanicalstrength effects of the bonded silicon carbide. Moreover, the roomtemperature service life characteristic can be enhanced, for example,the capacity of over 1400 mAh/g, the efficiency of over 98%, and theservice life of over 80% can be obtained. The initial efficiency is80˜95% and the anode initial efficiency is 85˜99.5%, which mean that theinitial charging and discharging characteristics can be also enhanced.

The embodiments of the lithium secondary battery according to thepresent invention will be described in detail, but the right scope ofthe present invention is not limited by such embodiments.

EMBODIMENTS AND EXPERIMENTS Embodiment 1

The organic solvent in the chamber may include a methanol. A pair ofelectrodes made of a stainless steel are installed. The silicon wafer ofa thickness of 0.8 mm is cut at an interval of a width of 1 mm and alength of 100 mm, thus forming a rod. The silicon nanocompositedispersion is prepared using a capacitor charged with the voltage of 11kV. As seen in FIGS. 2, 3, 4 and 5, it is confirmed that a siliconcarbide bonding or a carbon layer-coated silicon nanoparticle isprepared.

The silicon nanocomposite dispersion is filtered with a stainless steelmesh, and a centrifugation is carried out at 11000 rpm, thus preparing asilicon nanoparticle slurry.

The high temperature heat treatment of the slurry is carried out for 3˜5hours at 1100° C. under an argon environment, and it is subjected to adisintegration process, a dispersion process and a classificationprocess, thus preparing a silicon nanocomposite nanoparticle powder.

A coin battery with a diameter of 20 mm and a height of 3.2 mm isprepared using 80% by weight of an anode active substance containingover 5% by weight of the silicon nanocomposite powder for an anodeactive substance, 10% by weight of a super-p conductive material and 10%by weight of a PVDF binder.

Embodiment 2

The polyvinylrrolidone is added to the organic solvent including amethanol at 0.5 parts by weight with respect to 100 parts by weight ofthe whole organic solvent. The other procedures are carried out same asthe embodiment 1 except that the capacitor charged with the voltage of11.5 kV is used, and the heat treatment is carried out at 1150° C. underan argon environment, and then a disintegration process, a dispersionprocess and a classification process are carried so as to make a powderlump which is hold together with the nanocomposite of the size of 1-500μm.

Comparison Example 1

This is referred to a coin battery made of a silicon by Shin-etsu Co.Ltd.

The silicon by Shin-etsu Co. Ltd. is a silicon in which a siliconcarbine and a carbon layer are not included.

The TEM photo in FIG. 2 is referred to a photo wherein SiC is partlybonded to a silicon nanoparticle, and a graphite layer and a carbon arebonded. FIG. 3 is a view showing a result of the analysis of a silicon,a silicon carbide, and a carbon layer, while showing a X-ray diffractionof a silicon nanocomposite active substance. FIG. 4 is a view showing alattice of a structure which separates a silicon and a silicon carbide.

FIG. 5 is a view showing a thickness of a silicon carbide which isbonded over a silicon nanoparticle.

FIGS. 6 to 8 are views showing a room temperature service lifecharacteristic of a lithium secondary battery made of a siliconnanocomposite anode active substance. FIG. 6 is a graph showing acapacity of a coin battery. In case of the coin battery which is acomparison example, if it is repeatedly subjected to a charging anddischarging cycle more than 100 times, the capacity is fast reduced;however in case of the coin battery of the embodiment 1 (OP_Si_201307)and the embodiment 2 (OP_Si_201309), the capacity is gradually reducedeven though it is repeatedly subjected to the cycle 100 times. Accordingto the embodiment 2, even though it is repeatedly subjected to the cycle100 times, the capacity maintains over 1400 mAh/g.

FIG. 7 is a graph showing the efficiency (%) of the coin battery. Itshows that both the embodiments 1 and 2 have higher efficiencies thanthe comparison example.

FIG. 8 is a graph showing the capacity preservation ratio (%) of thecoin battery. If the coin battery which is a comparison example, isrepeatedly subjected to a charging and discharging cycle, the capacityis fast reduced. If it is repeatedly subjected to the cycle 100 times,the capacity preservation ratio is below 40%, and in case of the coinbattery of the embodiments 1 and 2, even if it is repeatedly subjectedto the cycle 100 times, the capacity is gradually reduced. In case ofthe embodiment 2, even if it is repeatedly subjected to the cycle 100times, the capacity preservation ratio maintains over 80%, and theembodiment 1 maintains over 75%.

FIG. 9 is a view showing an expansion inhibition level of a siliconnanocomposite anode based on a physical and mechanical high strengtheffect and a durable carbon layer of a silicon carbide bonded to asilicon nanoparticle when charging and discharging a coin battery. Incase of a lithium secondary battery which uses a silicon anode, a volumeexpansion may occur due to the chemical bonding between a silicon and alithium when charging and discharging. This theoretical expansion ratiois about 100˜400%, but the anode of the lithium secondary batteryaccording to the present invention may allow to reduce the anodeexpansion ratio to 10˜50% as the physical and mechanical high strengtheffect from the bonded silicon carbide and the durable carbon layersfunction to further inhibit the expansion of the silicon core. In thisway, the silicon anode blending content can be increased.

FIG. 10 is a view showing an initial charging and dischargingcharacteristic of a coin battery. In terms of the charging anddischarging characteristics, the initial charging capacity of thelithium secondary battery according to the present invention is2500˜3000 mAh/g, and the initial discharge capacity is 2000˜2500 mAh/g,and the initial efficiency is 80˜95%, and the anode initial efficiencyis 85˜99.5%.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described examples are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the meets and bounds of theclaims, or equivalences of such meets and bounds are therefore intendedto be embraced by the appended claims.

The invention claimed is:
 1. A silicon nanocomposite consisting of: asilicon nanoparticle having an average diameter of 100-300 nm; and asilicon carbide bonding which is configured on at least one region of asurface of the silicon nanoparticle with a thickness of 0.1-0.5 nm,wherein: a surface area where the silicon carbide bonding is formed, ascompared to a whole surface area of the silicon nanoparticle, accountsfor 10-50%, and a surface of the silicon nanocomposite further includesa carbon layer of a thickness of 3-15 nm.